Many waste streams from industrial chemical plants can cause continuous waste disposal problems in addition to cost inefficiency from the loss of raw materials.
Monocyanopyridines such as 2-, 3- and 4-cyanopyridines are well known starting materials used in the preparation of various chlorinated pesticides. Such pesticides include 3-chloro-2-cyanopyridine, 4,6-dichloro-2-cyanopyridine, the isomeric dichloro-difluoro-2-cyanopyridines, the isomeric trichloro-fluoro-2-cyanopyridines, tetrachloro-2-cyanopyridine, 2,6-dichloro-3-cyanopyridine, tetrachloro-3-cyanopyridine, 2,6-dichloro-4-cyanopyridine, among others.
such compounds, their preparation by vapor phase chlorination and their uses are taught in U.S. Pat. Nos. 3,317,549: 3,420,833; 3,629,424: 3,575,992 and 3,591,597.
The 2-, 3- and 4- cyanopyridines (hereinafter called cyanopyridines) employed in the present application are normally prepared by ammoxidation of the corresponding methylpyridine (.alpha., .beta., or .gamma. picoline) as taught in Abramovitch "Pyridine and its Derivatives", Part 2, 1974 (page 310), U.S. Pat. No. 3,637,715, Japan Nos. 7434673 and CA 77:139752e. The product is normally only one of the isomers.
The cyanopyridine feed stream prior to its use in vapor phase chlorination processes is first dried using molecular sieves to remove excess water and other by-products including the corresponding amide. The cyanopyridine feed stream is then vaporized. The non-vaporized bottoms from this procedure and the material removed from the molecular sieve during regeneration are combined. These combined materials make up the waste stream of the present specification and claims. This waste stream is primarily composed of cyanopyridine (about 70 percent of the waste stream), water, iron, the corresponding pyridine carboxamide, dimers, trimers and tar.
Currently, the valuable cyanopyridine in the waste stream is recovered by vacuum distillation of said stream. While the waste stream is rich in cyanopyridine, its recovery is reduced since any water present tends to hydrolyze some of the cyanopyridine to the corresponding amide and the iron in the stream catalyzes further degradation. Using the vacuum distillation procedure, only about 50 percent of the cyanopyridines present in the stream are recovered. After the distillation step, the residue remaining is usually disposed of by burning.
There is a need for a more economical and efficient procedure for recovering cyanopyridines from waste streams thereby reducing the loss of this desirable material.
The present invention discloses a novel and unobvious method for recovery of approximately 85-90 percent of cyanopyridines from a waste stream by low temperature chlorination of the waste stream followed by filtration. This process increases recovery of raw materials and significantly reduces waste stream volume.